Power transmission



'Aug."2 Z, 1944. A H. L.. wisE 2,356,366

- PowERTRANsMIssIQN K Filed Dec. 4, 1942 f s sheets-'sheet 1 DEEE-5L "f f,

- INVENTOR ATTORNEYS Aug. 22, 1944. H. l.. WISE 2,355,355

y vPOWER TRANsMssoN Filed De@l 4, '1942 Smeets-sheet 2 INI 'ENTOR Haag/. Wwe,

- Aug. 22,1944.

l H. L. WISE POWER TRANSMISSION I INVENTOR. /lzrrrg ,Wz'eg f inafter set forth.

, present invention;

Patented Aug, 22, 1944;t

POWER TRANSMISSION i Harry L. Wise, Detroit, Mich., assignor to Hydraulic Machinery, Inc., Detroit, Mich., a corporation ot Michigan Application December 4, 17942, Serial o. 1677,834*` `9 Claims. (Cl. 121-33) The present invention relates to pOWer transmission, and particularly relates to a fluid pressure power transmitting and control device.

One of the primary objects of the. present invention is. to transmit fluid power to a fluid motor and to control such transmission in animproved manner.A l

4A further;v object of the present invention is to control the supply 'of iiuid to a reciprocating motor at two diferentpressures, atderent stages in the operation of the motor.

. Y Aiurther object of the invention is to control.

the vsupply of `fluid to a reciprocating motor at v highand low pressure so that the motor piston isvmoved to a work position at the low pressure, the high pressure then admitted to do the work, and the piston returned at the low pressure. i

n A further object ofthe present invention is to .control the supplyy of fluid to a reciprocating motor atv low and high pressures so that a diierential Lfeed'is employed to move the piston to In general, the power transmission system of the present invention embodies the control of iiow of a fluid from a `low pressure source and from a high pressure source to a fluid operated riveting gun. In the embodiment illustrated, the

A low and high pressure sources are low and high the work position at the low pressure and high Y y speed, the high pressure then admitted to do the work, and the piston returned at ther lowy pres.

-, sure.

returns to its initial position, the cycle cannot repeat until the button is first released. l

Other objects of the invention lwill become appressure accumulators from which the fluid is conducted to the riveting gun through a supply line havingvthe uidcontrol panel of the present invention combined therewith. The fluid control panel of the `present invention employs a plurality of valves which are so constructed and yarranged that upon the ,energization of a solenoid by a push button on the hammer, the low pressureis introduced to the gun to move the work element from a retracted position to a vwork position at the low pressure and at a relatively high speed. The conduits in theL control panel and to the gun are such that a differential feed of the piston is accomplished, so that the work element moves to a work position `at a relatively high speed, but at the low pressure.. Pilot means are constructed in the control panel so that when the piston is moved to its worlc position the valves are shifted so that the low pressure supply iscut off and the high pre'ssire supply is openedtd f eed the high pressure uid to thefree end of the piston to do the Work at the parent from the following specification, the draw-v ings relating thereto, and from the claims here- In the drawings, in which like numerals. are

' used to designate like parts in the several views high pressure. The pilot means then act to deenergize the solenoid so that the ysolenoid valve is shifted and low pressure fluid acts to return cer- V`tain of the valves to theirinitial position to cut oil the supply of high pressure fluid to the gun `and to return the gun piston to its original posiis generally indicated at I0, which includes a fluid motor' comprising a v'cylinder I2 and a piston I 4,

Figure 2 is a cross-sectional view of the conl trol panel employed in the system shown in Figure l, embodying features of the present invention, and showing such rcontrol panel in its ashaving a piston rod I6 associated therewith and projecting through one 'end of the cylinder I2. The.l piston rod I6 may be considered the work element. The cylinder I2 is provided with ports I Il and 20, at the opposite ends thereof and on opposite sides of the piston Il. The gun I0 is of conventional construction.

The fluid under pressure is supplied from la tank or reservoir 22 which contains a suitable supply of fluid, preferably oil. A low pressure pump Mis driven by a suitable prime mover 26,' which may be an electric motor,v the inlet of the pump being inr communication with the to the pump for recirculation. The conduit 30 leads to a, low pressure accumulator 36 through a branch conduit 38 and has an unloading valve 40 and a check valve 42 associated therewith and located in the order named between the overload relief valve 32 andthe accumulator 36. The check valve 42 permits the flow of low pressure uid to the low pressure accumulator but prevents the return of iiow through conduit 30. A conduit 44 is connected to the accumulator conduit 38 and to an inlet port in the control panelV generally indicated at 46, for th'e supply of low pressure from the accumulator 36 to the control panel 46. The low pressure supplied to the panel 46 may be at 1000 lbs, per square inch, for example.

Suchvalve 32 is of, conven- Ytion of spool 16. Port 12 of Valve 68 communicates with port 80 of valve 66 through conduit A lhigh pressure pump 48 is also associated sure, and which are indicated by similar primed numerals.

The high pressure uid from the'accumulator 50 may be at 5000 lbs. per square inch, for example, and is' 'supplied to the control panel'` 46 through a conduit 52 which communicates with the high pressure accumulatorconduit 38.

Low pressure is thereby supplied to the control panel 46 through the conduit 44 and high pressure uid is supplied to the panel 46 throughA conduit 52.

A conduit 54 communicates with" the interior of the cylinder I2 on the rod side of the piston I4; anda conduit 56 communicates with the interior of the cylinder I2 on the opposite side of the piston I4. The conduits 54 and 56 com municate with conduits 58 and-60, respectively, formed in the control panel 46 'through suitable ports in the walls thereof.

The control panel 46 comprises a, housing formed with control va'lves generally indicated at' 62, 64, 66, and 68. Valve 68 includes a bore 69 formed with ports 10, 12, and 14 therein and has a spool 16 reciprocably disposed therein. Port 10 is cored and is in direct communication with low pressure inlet conduit 44, and port 14 is in direct communication witha conduit 18 which returns directly to the tank.

Valve 66 includes a longitudinal bore 19 and is formed with ports 80,' 82, and 84 and has a reciprocable spool 86 disposed therein.

Valve 64 includes a bore 81 having ports 88, 90,' and 92 formed therein and has a reciprocable piston 94 disposed therein.

Valve 62 includes a bore 95 having ports 96 and 98 formed therein and having a reciprocable spool 99 disposed therein. The spool 99 has a reduced end portion |0| formed on one end thereof which `is received within a bore |02 formed in the'housing and which has a purpose to be described hereinafter.

A relatively light coil spring |04 is disposed between the opposite end of the spool 99 and the vmi ciprocably disposed therein.

|08. Port 90 of valve 64 communicates with port 98 of VValve 62 through conduit I|0. Port 96 of valve 62 communicates directly .with conduit 58.

Port 82 of valve 66 communicates with conduit 60, which communicates with conduit 58 leading to the free end of the cylinder `|2. Port 92 of valve 64 communicates with conduit ||2, which communicates with a conduit ||4 leading back tothe tank. Port 84 of valve 66 communicates with a conduit IIB, which communicates with a conduit 52 leading to the high pressure source.

Pilot means are .provided for automatically shifting the valves s2. s4, ss, and sa and foroperating the solenoid, and such pilot means include a pilot solenoid valve generally indicated at ||8. The valve I|8 includes a'borev having ports |20, |22,and |24 and has a spool |26 re- Spool |26 iscon- Anected to a. reciprocating shaft |28, which is connectedvto the movable element of a conventional solenoid |30. The solenoid |30 is connected to a suitable source of electric energy through an electric control panel, `described hereinafter, so that when the push button |32 on the gun I0 is actuated thesolenoid is energized to shift thespool |26 to the right to the position shown in Figure 2. v

Port |20 communicates `with a pilot` conduit |34, which c'ommunicateswith another conduit |36 formed in the housing adjacentthe lower ends of the bores 81, 19, and 69. Such passageway |36 is in open communication with the lower ends of the bores of the three valves mentioned.- Port |22 communicates with conduit |38 which communicates-with a conduit |40. Such conduit |40 may be a branch conduit from the low pressure conduit 44 and be in open communication therewith. Port |24 communicates with a conduit |42 which is in open communication with the upper end of the bore 95 of valve 62, and which is also in open communication with branch conduit I`44. The branch conduit |44 is in communication with the upper end of the bore 69 of. valve 68.

' Therlght end (viewing Figure 2) of the bore of pilot valve ||8 communicates with a. conduitr |46, which communicates with the tank through a conduit |48 and also communicates with the lower end of the bore of valve 62. The spool |28 ing through one end thereof and communicating with the conduit- |48. The spoolf|26 is also v formed with a plurality of radial apertures |5| Port of valve 66 is in communication with i a pilot conduit |52 which is in open communicationl with a chamber |54. Such chamber |54 is in communication with a pilot conduit |56 .fassasee l)throughs-ballcheck valves-|58 and-|60. Theball 'R4a isl open and holding circuit contact VR41: is

checks r|168 and |160 .function in opposite .directions, asshown in Figure .2. 'The conduit |56 ,isfin open .communication with a conduit |62 which -opensinto-'the upperfend (viewing Figure 2) of `the .borei95 fof `valve v64. The conduit I |56 is also in communication `with the upper end (viewing Figure 2) ofthe v.bore .19 of .valve vf.68.

i .A `restricting element` |64 isf disposed in Athe 'branch of the -conduitpl 56 leading tothe bore of valve .66 Aso ythat there will Lbe atime lag in the movement 4ofspool ...86, Vaswill be pointed yout hereinafter.

At `one .stage-of `the operation, the Ysolenoid is actuated -byna pressure switch 66 having `conduits `|68 .and *|10 .associated therewith. The `conduit returns tto adrain, while the .conduit '|68 communicates with :a plunger chamber |112 `formed inthe .control -panel 146. The .chamber A|12 .is @inthe lform ofqa cylindrical bore and yhas :avpiston Y|14 slidably `disposed therein.v .'I'herod end |16 of the vpiston ..|-|4 is slidably vreceived within achamber |80 .of reduced diameter. The .chamber |80 communicates with the stank .through a conduit. |:82.and the -end of thechamvber |80 communicates with conduit .60 lthrough a branch conduit |84;

'The conduit `44 communicates with the chamber` l'l2nthrough `a conduit .|86 which has aball check valve |'88Fdisposed therein and operable- .in .the direction indicated in Figure2. n

. Bore |02, .at the lower endr of spool99, vcommunicates ywith a :conduit |90 which communi Vcateswith conduit 0 through a conduit :|92 hav'-y ing a checkva'lve |94 therein. The conduit '|90 .also communicates with conduit |92 'through Vis conducted to the electric panel through suitable ;leads vfrom a suitable source. Motor start 'andA stop buttons are indicated at 20| and 202,

respectively. 'I'he'dlagram is illustrated with the operating elements in their non-operating positions. With the start `button 20| actuated to 'close .the circuit, coils or relays /Rland R2 areY energized to` close the normally" open', holding circuit contact Rla and to close the normally open contacts *R|b, .R|,c, .R2a, R2b, vand .R2c.

I Q When the start button 20| is released, the circuit will-.beheld 'through contact Ria.l The low pressure pumpv motor 226 and the high .pressure pump ymotor`26 will thus .operate to supply the closed. The r'button |32 is held closed bythe operator during the riveting operating, so thatv contacts R3a and R3b-remai`n closed.- When contact R4a is opened, solenoid |30 is de-energized,

so (that the spool |26 is shifted to the left, view- -de-energizingcoil R3. When coil R3 isde-ener- .gized,"contact R3a opens and contact R315 also opens, causing coil R4 tobecome de-energized.

and normally closed'contact R4a closes. The elements forthe control vof the solenoid .|30 vand the pressure switch |66 thusL return to their originalpositions, and the cycle may be repeated when the Aoperator closes push button |32.

1 vIn ythe operationof the enti-re 'fluid circuit, includingthevoperation'of the panel 46, whenv the push -button |32 is heldfclosed .by the` operator, which must be maintained throughf the entire compression of the rivet, the electric circuit acts as describedl above'to'shift the spool |26 to the position shown in Figurev 2. The pumps 24and 48 are, at the time, in operation to supplyfiuid to the low pressure accumulator 36 and the high- 46 through conduits 44 and 5,2, respectively...

lowand high pressure to the accumulators V-in o l the fluid circuit described above; When the stop button 202 is actuated, the circuit is opened, deenergizing coils R|..and.R2 thereby `opening .con-

.tacts .'Rla, .R|b, Ric, -'-R.|d,` R211 R2b,`and R21: to stop motors 28 Yand .26'. The motors are, of g course, operated during 4the `use of thefgun I0.

Whenthe push button |32 isactuated to oper- .ate the-gun'l, the'circuitisfclosed to energizecoil or relay R3. Normally open contacts R3a yand R3b arethen closed. Normally closed contact R4a remains closed and the solenoid |30 isV energized to'shift the spool |26 to the Tight to the position" shown in Fig. 2.' vThe panel 46 then operates |66 is closed to energize relay or Acoil R4. When l coil R4 is energized,"normally closed contact vWith the spool |26 in the position shown in Fig. 2,low pressure fluid enters conduit |40 and passes into conduits |42 and |44 through ports |22 andl24. Spools199 and '|6 are then moved to une positions shown in Figure 2. spools at' and 86 remain in the 'positions shown in Figure 2. As'the lspool 99 moves downwardly, the fluid in the lowerr end of the bore exhausts to tank through `conduits |44, |46, and |48; and the vfluid under the reduced end |0| exhausts through'con- .duits |90, check valve |98, and conduits `|96 and |92 into conduit ||0.` The iluid may flow .from

vconduit ||0 along with the iluid from line |54,

as will be pointed out hereinafter.

The fluid under spool 16 passes through contures lsllnto the boro Maand back to. the tank through conduits |46 and |48.l

With the spools in the positions described, high oi.' port y82 into conduit 60, `and from there into lconduit 56 to the cylinder throughport I6. The

conduit 44 is, vat the same "time, open to conduit 64. but, due tothe differential totall pressures acting on the opposite sides of the piston |4, such piston will move in the direction of the arrow on rod |6. The fluid inthe cylinder rI2v on the vrod side of the pistonwill then ilow throughconduit 64, in the directiomof the arrowsy of Fig. 2,

4through conduit ysa, into 'port 96,. out of .port sa, y into conduit ||0, 'into port 90out oi port 88,'

into conduitIB, into port ,10, and out of port 12 along with the-fluid from .conduit 44. Such iluid also kcarries with it the fluid from conduit |92. This'. differential feedA gives a relatively high speed feed of the Vpiston 4I4 to the work position at a low pressure.

When the piston I4 moves to the work position in the direction indicated andl against the work, the pressure in pilot line |52, whichcommunicates with the low pressure line through port 80, builds up to a predetermined panel 'setting depending upon the adjustment of a check valve |58 to open check valve |50 and pass fluid into conduits |56 and |62. Passage of the fluid into these conduits causes spool 94 to move downwardly to the bottom of'bore 81, and this shuts off communication between conduits |06 and IIO. Fluid from one branch of conduit |56 passes through restriction |64 to cause spool 86 to move downwardly to thebottom of bore 19. Fluid under spools 94 and 86 returns to the tank through conduit |36, conduit |34, apertures I bore |49, and conduits |46 and |48. f

With the spools 94 and 86 in the down position just described, the supply of low pressure fluid Y from .conduit 44 is cut oil' to the cylinder I2 by spools 86 and 94. Howevenhigh pressure fluid from conduit 52 then passes through conduit I|6 into port 84 of valve 66 and out of port 82 into conduit 60. 'I'he fluid passes from the conduit 60 through conduit 56 and into the cylinder vI2 throughV port I8, so that'the Work is done at the high pressure. Fluid may then exhaust from the rod side of the piston I4, through conduits 54 and 58, into port 96 of valve 62, out of port 98 into conduit I0, into port 90 of valve 64, out of port V92 and into conduit` II2, which returns to the'tank through conduit I I4. Y

The operating plunger |14, which operatesthe pressure switch |66, is held in the position shown in Figure 2 by the low pressure'from line 44 through conduit |86 and check valve |88. As the high pressure fluid builds up in conduit 60 at the end of the work stroke or due to the resistance to riveting pressure, such fluid passes into chamber |80 and moves the plunger |14 to the right, viewing Figure 2. The fluid within chamber |12 then passes through conduit |68 to the pressure switch |66, and actuates such switch to de-energize the solenoid |30, as described above.

When the solenoid |30 is de-energized, the spool |26 moves to the left, viewing Figure 2, and low pressure fluid enters through conduits |40 and |38 into port |22 and outof port |20 into conduit |34. Such fluid then acts through conduit |36 to shift spools 94, 86, land 16 to their upper positions. When spool 86 is in its upper position, the flowof high pressure fluid from conduit 52 is cut ofi from flow to conduit 60. Fluid within the bores above spools 94 and 86 exhausts through conduit;l |56, check valve |60, conduit |52, conduit I08,*into port 12 of valve 68 and out of port 14 into conduit 18, which returns to the tank.

As thev spool 'I6 moves to its upper position, the fluid in the bore above thev spool exhausts through conduits |44 and |42, into port |24, and to the'tank through conduits |46 and |48.

When the plunger 16 is in its upper position, theflow pressure line 44 is still in communication with the conduit |06 through the cored port 10, which surrounds 'the lower portion of the spool 16 in spaced relation thereto when such spool is in its upper position. The low pressure fluid from conduit |06 then passes through valve 64 into4 conduit |I0, and from conduit I|0 through valve 62 into conduits 58 and 54. The fluid enters the cylinder |2 through port 20 and forces the piston I4, together with the rod I6, toits retracted position. When the piston I4 reaches its limit of movement, pressure builds up in conduit I|0 to a predetermined panel setting depending upon the adjustment of check valve |94, andJ the fluid flows from such conduit I I0 through conduit |92, through check-valve |94, into conduit |90 and acts upon the lower reduced end |0I of the spool 99 to move such spool upwardly. The fluid above the upper end of spool 99 exhausts through conduit |42, port |24, and conduits |46 and |48.

When the spool 99 moves upwardly, the flow of .A low pressure fluid is cut off tothe rod end of the cylinder. This isthe end of the cycle,and, when the solenoid is again energized, the cycle is repeated. Y

The terms upper and lower, as used above, are not intended to be limiting, but are merely used in a descriptive way to indicate relative positions yon the drawing illustrations.

What is claimed is:

1. In afluid power transmission for driving a reciprocating fluid motor .including a'cylinder, piston and piston rod,.the combination of first means providing a sourceof fluid `at one pressure, second means providing a source of fluid at another pressure, fluidsupply and return connections between said first and second means and the motor, andcontrol means disposed in said connections for controlling the operation of said motor, said'controlmeans including valve kmeans to admit fluid from said first means to said cylinder to advance said piston to'one position, pilot means responsive to the pressure from said first means upon a predetermined pressure rise due to resistance to advance of said piston to shift said valve means so as to admit fluid from said second means to said cylinder to fur.- ther advance said piston, and pilot means actuated in response to the pressure from said second means when the/pressure in the high pressure line reaches a predetermined value to shift said valve means to cut off flow from said second means to said cylinder and to admit fluid from said first means to said cylinder on the opposite side of the piston. K

2. In a fluid power transmission for driving a reciprocating fluid motor including a cylinder, piston andpiston rod, the vcombination of first means providing a. source of fluid at relatively low pressure, second means providing a source of fluid at relatively high pressure, fluid supply and return connections between said rst and secondl means and the motor, and control'means disposed in said connections for controlling the operation of saidmotor, said control means including valve means to admit fluid from said first means yto said cylinder to advance said piston to one position, pilot means responsive to the pressure from said first means upon a predetermined pressure rise due to resistance to advance of said piston to shift said valve means so as to admit lfluid from said second means to said cylinder to further advance said piston, and pilot means actuated in response to the pressure from said second means when` the -pressure in the high pressure line reaches a predetermined'value to shift said valve means to cut off flow from said second means to said cylinder and to admit fluid from said first means to said cylinder on the opposite side of the piston.

3` In a fluid power transmission for driving a reciprocating fluid motor including a cylinder, piston and piston rod, the combination of first means providing a source of fluid at relatively low pressure, Second means providing a SOLlICe Of posed in said connections posed in said connections for controlling the operation of said motor, said control means including valve means to admit fluid from said first means to said cylinder to advance said piston to one position, pilot means responsive to the pressure from said first means upon a predetermined pressure rise due to resistance to advance of said piston to shift said valve means so `as to admit uld from said second means 'to saidv cylinder to further advance said piston, and electrically operated pilot means actuated in response to .the pressure vfrom said second means when the pres-- sure in the high pressure line reaches a predetermined value to shift said valve means to cut of! ilow from said second means to said cylinder and to admit uid from said first means tosaid cylinder on the opposite side of the piston.

4. In a fluid power transmission for driving a reciprocating fluid motor including a cylinder, piston and piston rod. the combination of first means providing a source of fluid at relatively low pressure, second means providing a' source of flud at relatively high pressure, fluid supply andreturn connections between said first and second means and the motor; and control means disfor controlling the opsaid control means including a plurality of valves, electrically responsive pilot means to shift certain of said valves to ad, mit fluid from said first means to said cylinder to advance said piston to one position when said pilot means is in one position, pilot means responsive to the pressure from said rst means upon a predetermined pressure rise due to resistance to advance of said piston to shift certain of said valves so as to admit uid from said second means to said cylinder piston, and pilot means actuatedgin response to the pressure from said second means when the pressure in the high pressure line reaches a predetermined value to shift said first named pilot means to another position to thereby shift certain of said valves to cut off flow from said second means to said cylinder and to admit fluid from said rst means to said cylinder on the opposite side of the piston.

5. In a fluid power transmission for driving a reciprocating fluid motor including a cylinder, piston and piston rod, the combination of first means providing a source of fluid at relatively low pressure, second means providing a source of fluid at relatively high pressure, fluid supply and return connections between said first and second means and the motor, and control means disposed in said connectionsv for controlling the operation of said motor, said control means including valve means, electrically responsive pilot means to shift said valve means to admit fluid from said first means to said cylinder to advance said piston to one position when said pilot means is in one position, pilot means responsive to the pressure from said first means upon a predetermined pressure rise due toresistance to advance of said piston to shift said valve means so as to admit fluid from said second means to said cylinder to further advance said piston, and a pressure switch actuated in response to the pressure from said second means when the pressure in the high pressure line reaches a predetermined value to aect operation of said first named pilot means to shift said first named pilot means thereby shift said valve means to cut off flow from said second means to said cylinder on the opposite side of the piston.

eration of said motor,

to another position to to further advance said .-6. In a fluid power transmission for driving a reciprocating fluid motor including a cylinder, piston and piston rod, the combination of rst 'means providing a source of fluid at relatively low pressure, second means providing a source of fluid at relatively high pressure, fluid supply and return connections between said first and second means and the motor, and control means disposed in said connections for controlling the operation of said motor, said' control means includingvalve means open to admit fluid from said first means to both ends of said cylinder to obtain a differential advance of said piston to one position, pilot means responsive to the pressure from said first means upon a predetermined pressure rise due to resistance to advance of said pistonto shift said valve means so as to admit uid from said second means to said cylinder to erating element, the combination of first meansproviding a source of fluid at relatively low pressure, second means providing a source of fluid at relatively high pressure, fluid supply and return connections between said first and second means and the motor, and control means disposed in said connections for controlling the operation of said motor, said control means includingvalve means, solenoid pilot means to shift said valve means to admit fluid from said ilrst means to said cylinder to advance said piston to one position when said pilot means is in one position, pilot means responsive to the pressure from said first means upon a predetermined pressure rise due to resistance to advance of said piston to shift said valve means so as to admit fluid from said second means to said cylinder to further advance said piston, a .pressure switch actuated in response to the pressure from said second means when the pressure in the high pressure line reaches a predetermined value to de-energize said solenoid pilot means to shift said first named pilot means to another position to thereby shift said valve means to cut off flow from said second means to said cylinder and to admit fluid from said first means to said cylinder on the opposite side of the piston, and means forming an electric circuit operable upon actuation of said operating element to energize said solenoid pilot means to initiate the cycle of operation of the control means, said electric circuit being such that a cycle of operation cannot repeat without releasing said electric operating element.

8. A control panel for use in a fluid power transmission system for driving a reciprocating fluid motor at a low pressure and a high pressure, including a housing having a. plurality of valves therein, means to admit iluid from said rst means to said cylinder to advance said piston to one position, pilot meansv responsive to the pressure from said first means upon a predetermined pressure rise vdue to resistance to advance of said piston to shift said valve means so as to admit fluid from said second means to said cylinder to further advance said piston, and pilot means actuated in response to the pressure from said second means when the pressure in the high pressure reaches a predetermined value to shift said valve means to cut of! flow from said second means to said cylinder and to admit 'fluid from saidfflrst means to said cylinder on the opposite side of the piston.

9. A control panel for use in a fluid power transmission system for driving a reciprocating fiud motor at a low pressure and at akhigher pressure comprising a housing having a. pluraity of valves therein, electrically responsive pilot means to shift certain of said valves to v 7 admit low'pressure yfluid from onesource, pilot means responsive toa predetermined pressure value of the low pressure uid to shift certain A of said valves so as to vadmit'. higher pressure 5 :duid from another source, and pilotrmeans ac- 10 iiow from said another source and to 'admit i'iuid from said one source. Y

f vHARRY L WISE.

.Patent No. 2,556,566.

CERTIFICATE 0F CORRECTION. v

l August 22, 19h14.

i y HARRY'L. wIsE.

It 1s hereby certified that error appears vinthe printed specification of the above numbered patent 'requiring correctionas follows.: Page 6, first that the said; Letters Patent should be read lwith thi'oorrection therein that the same nay conform to the record of the case in the-Patent Office.

signed and .sealed this 101111 day of october, VA; D. 19141;.

. Henry Van Aredale (Seal) Acting Commsioner, of Patents. 

